UK Prime Minister Sir Keir Starmer has been reported to the International Criminal Court (ICC) for alleged crimes against humanity in connection with his government’s controversial Chagos Islands agreement with Mauritius.
The complaint was filed on Monday evening by a group of indigenous Chagossians who argue that the deal continues the historic forced displacement of their community. The group has also named Foreign Secretary David Lammy and Defence Secretary John Healey in the referral.
The campaigners accuse the UK government of perpetuating deportation or forcible transfer of population by denying native Chagossians the right to return to Diego Garcia, the largest island in the Chagos archipelago and home to a major military base.
Criticism of the deal has come from Chagossians, Conservative Party members, and Reform UK, all of whom oppose the decision to transfer sovereignty of the Chagos Islands to Mauritius. The move follows decades of international legal challenges by Mauritius, which claims the islands should have been returned when it gained independence from Britain in 1968.
Instead, the UK retained the territory, designating it as the British Indian Ocean Territory (BIOT). Between 1968 and 1973, native islanders were forcibly removed to make way for the construction of the joint UK-US military base on Diego Garcia, an act widely condemned as a breach of international law. Many of the displaced Chagossians later resettled in the UK.
Although the new agreement allows Mauritius to reclaim sovereignty over the islands later this year, it also permits the UK to lease back Diego Garcia, ensuring continued military use. However, campaigners argue that the deal does not guarantee the return of native islanders, effectively extending their decades-long displacement.
The ICC referral has labels the original expulsions “one of the longest-standing and most egregious cases of displacement in modern history” and claims the UK Government has “knowingly perpetuated crimes against humanity.” Victims, it adds, have “waited half a century for justice.”
The complaint is spearheaded by Bertrice Pompe, a native of Diego Garcia who has previously challenged the Chagos deal in UK courts. In May, she temporarily halted the signing of the treaty through an emergency injunction, though it was later overturned.
In a statement, Pompe urged international intervention,“We are pleading with all those who have the power to make a difference to please step in and stop these crimes against humanity. We are the indigenous of the Chagos Islands, we bear their name, and we need our voices to be heard.”
While the Chagos agreement states that Mauritius is “free to implement a programme of resettlement,” campaigners argue this is non-binding and insufficient.
An open letter addressed to ICC Prosecutor Karim Khan was also released, urging the court to launch a formal case against the Prime Minister and his ministers. The letter claims that by signing the agreement on May 22, 2025, the UK Government has entrenched “deportation, persecution and other inhumane acts.”
It further alleges,“While it may be difficult or impossible to investigate the original perpetrators from the 1960s and 1970s, it is both possible and necessary to investigate those who now perpetuate the crime.”
The letter criticises Lammy for negotiating the agreement and Healey for defending the exclusion of Chagossians on security grounds.
The ICC will now consider whether to open a preliminary investigation. If sufficient grounds are found, the court may proceed with a full inquiry into potential crimes against humanity.
Neither the Foreign Office nor the ICC has issued a comment on the matter.
